This invention relates to a process for preparing olefin polymers using novel catalyst kill agents and/or neutralizers. Olefin polymers such as polyethylene and polypropylene are often produced by use of a transition metal polymerization catalyst thereby leaving small amounts of catalyst residues in the polymer. Such residues are typically thereafter deactivated to prevent continued polymerization and the deactivation products neutralized to reduce color body formation or corrosion due to the presence of hydrochloric acid or other by-products. This is normally accomplished by mixing one or more additives with the polymer while in a molten state or in the polymer containing product stream exiting a polymerization reactor prior to devolatilization.
A wide variety of deactivating agents have been utilized or disclosed in the prior art, generally hydroxyl group containing compounds, including water and water releasing compounds, optionally in combination with a neutralizer, including alcohols, phenols, diols, polyols, saccharides, ethers, epoxides, aldehydes, ketones, carboxylic acids, diacids and polyacids, their anhydrides, esters or salts, polyalkylene glycols, and amines; fatty acid salts; alcohols; polyalkylene glycols; polyvinyl alcohols; aliphatic alcohols; and salts of poly(oxyalkylene) compounds. References disclosing the foregoing include EP-67,645, EP-71,252, GB-2,132,214, EP-A-140131, WO92/14766, and WO03/55920.
Typically acid neutralizers and similar compounds are added in a two step process first employing a catalyst “kill” agent, such as water or an alcohol, followed by incorporating the neutralizer to scavenge acid species in the reaction mixture. Generation of strong acid residues, even for short periods, and subsequent removal by reaction with a scavenger has proven to be problematic due to exposure of the polymer at elevated temperatures within the recovery section of the reactor to the acid residue of the catalysts and inability to thereafter efficiently extract or neutralize such acid species. This can cause small quantities of acid, especially HCl, to become entrained in volatile components of the mixture and become incorporated into the recycle stream, leading to corrosion of recycle equipment. Additionally, typical acid neutralizers have proven to be susceptible to decomposition or oxidation over prolonged periods. Certain of the compounds additionally tend to separate from the polymer and migrate to the polymer surface during subsequent melt forming processes where they interfere with desired surface properties or esthetics of the polymer article or react with additives or other components of desired polymer blends or compositions. Finally, due to the relative inefficiency of previously known acid scavengers, excessive quantities thereof have been required in order to adequately reduce levels of catalyst residue in the polymer and acid species in the recycle stream. Accordingly, further improvement in polymer additives, especially acid neutralizing additives are desired. In particular, the attainment of equivalent or improved performance with reduced quantities of additives and, optionally, the use of a single component to achieve catalyst deactivation without generation of acidic by-products requiring further neutralization is desired.
U.S. Pat. No. 5,840,422 disclosed the use of ionomers as acid scavengers in blends of fluoropolymers with polyethylene. Other references disclosing use of ionomers to scavenge acidic species in polymeric compositions include U.S. Pat. No. 5,707,569 and U.S. Pat. No. 5,445,893. Adding ionomers to a process stream prior to devolatilization or use of an ionomer as a combination catalyst kill and acid neutralizer is not disclosed.